JPS5834812B2 - soft focus attachment lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a soft focus attachment lens that is attached to the object side of a main lens to change spherical aberration.

Lenses designed specifically for soft focus have the disadvantage that they are difficult to focus on with cameras that use focusing plates, such as reflex cameras.

Furthermore, when a soft focus lens is used as a general photographic lens, it must be stopped down to reduce spherical aberration, which is dark and inconvenient.

Lens systems that solve the above drawbacks by moving a part of the lens system are known, but the structure of the lens frame is complicated, adjustment is difficult, and the cost is very high.

By attaching this invention to the object side of a general photographic lens, it can be used to improve
To provide a soft-focus attachment lens with an extremely simple configuration that generates a large amount of high-order spherical aberration and whose focus position does not change even when the attachment lens is attached.

The attachment lens of the present invention is composed of two lenses, a concave lens and a convex lens, and these two lenses form a concentric air gap with the concave surface facing the aperture to eliminate high-order spherical aberration. The lens is configured so that it is afocal, and the angular magnification is approximately 1, so that the focus position does not change even if the attachment lens of the present invention is attached after focusing only with the main lens. It is something.

The present invention will be explained in detail below with reference to FIGS. 1 to 4.

FIG. 1 is a configuration diagram of only the main lens used in Example 1 of the present invention, and numerical examples thereof are shown in Table 1, and aberration coefficients are shown in Table 2.

FIG. 2 shows the spherical aberration, astigmatism, and distortion of the main lens.

Next, FIG. 3 shows a configuration diagram when the first embodiment of the present invention is attached to the object side of the main lens.

In Example 1, an IJ rack air gap is provided (with a concave surface facing the aperture), and of the two surfaces that sandwich the air gap, the object side surface is rA, and the image side surface is rA. By configuring the structure to satisfy the following conditions, a large amount of high-order spherical aberration is generated, and by setting the distance from rA' to the aperture of the main lens as ΣdA, by satisfying the following conditions, rA This soft focus attachment lens is characterized in that the center of curvature of and r A / is placed near the aperture of the main lens so that various aberrations other than spherical aberration are not generated from the attachment lens.

Numerical examples of Example 1 are shown in Table 3, and aberration coefficients are shown in Table 4.

FIG. 4 shows an aberration diagram of Example 1.

In order to know whether higher-order spherical aberration has been effectively generated by attaching an attachment lens, it is necessary to calculate the sum of the third-order spherical aberration coefficients Σ■ and the fifth-order annular spherical* aberration due to attaching the attachment lens. Just look at the change in the sum of coefficients Σ■.

In Example 1, it is as follows.

However, Σ■A: Sum of the third-order spherical aberration coefficients of the main lens only Σ■B: 3 of the composite system of the main lens and attachment lens
Sum of order spherical aberration coefficients* Σ■A: Phase of 5th order annular spherical aberration system of main lens only* Σ■B: 5 of composite system of main lens and attachment lens
If the sum of the order annular spherical aberration coefficients is 100 or more, it can be said that the higher-order spherical aberration can be changed significantly without changing the third-order spherical aberration much.

In the embodiment of the present invention, the attachment lens is configured to be an afocal system with an angular magnification of 1, so even if the attachment lens is attached or detached, the focal length and back focus of the composite system remain paraxial. , the best image plane moves slightly because the spherical aberration changes.

Therefore, in reality, it is better to configure the lens so that the focal length and best image remain unchanged when the actuation lens is attached or detached.

[Brief explanation of drawings]

1 and 2 are block diagrams and aberration diagrams of only the main lens used in Example 1, and FIGS. 3 and 4 are block diagrams and aberration diagrams of Example 1.

Claims (1)

[Claims] 1. Mounted on the object side of the main lens configured to satisfy the following conditions, where t is the axial distance from the first surface of the main lens to the aperture, and R is the radius of the aperture when fully open. As an attachment lens, it uses a single concave lens and a single convex lens, making it highly afocal with an angular magnification of approximately l.
The radius of curvature of the image-side surface of the concave lens and the object-side surface of the convex lens are rA and rA', respectively.
, where the axial distance from the object-side surface of the convex lens to the aperture of the main lens is ΣdA.